CHEM 1B Chapter Notes - Chapter 14: Boiling-Point Elevation, Molality, Osmosis

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Published on 18 Aug 2016
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UC-Irvine
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Chemistry
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CHEM 1B
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Chapter 14: Solutions
14.1 Antifreeze in Frogs
Concentrated solutions have a lower freezing point then pure liquids
Solution = a homogeneous mixture of two or more substances or components
Solvent = the majority component
Solute = the minority component
Particles of the solvent interact with particles of the solute through intermolecular forces
14.2 Types of Solutions and Solubility
Aqueous solutions = water is the solvent, and solid, liquid, or gas is solute
Solubility = the amount of the substance that will dissolve in a given amount of solvent
Nature’s Tendency Toward Mixing: Entropy
Systems tend toward lower potential energy
Formation of a solution does not necessarily lower potential energy of constituent particles
We cannot think of the missing of two ideal gases as lowering their potential energy.
Entropy = measure of energy randomization or energy dispersal in a system.
When the barrier is removed the gases have more dispersal or entropy than when separated
The pervasive tendency for energy to spread out, or disperse, whenever it is not restrained from
doing so is the reason two ideal gases mix.
Energy does not spontaneously concentrate itself
The Effect of Intermolecular Forces
Intermolecular forces between (a) solvent and solute, (b) solvent particles themselves (c) solute
particles themselves.
miscible = the two substances are soluble in each other, have interactions of same magnitude
If disparity is small the tendency to mix results in a solution, if large then no solution is formed
Polar solvents tend to dissolve many polar or ionic solutes, nonpolar solvents dissolve nonpolar
14.3 Energetics of Solution Formation
Energy Changes during Solution Formation
1. Separating the solute into its constituent particles > 0
2. Separating the solvent particles from each other to make room for solute particles
3. Mixing the solute particles with the solvent particles
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Enthalpy of solution = sum of the changes
=
If the sum of the endothermic terms is approximately equal in magnitude to the exothermic
term, the is about zero
If the sum of the endothermic terms is smaller in magnitude than the exothermic term, then is
negative and the solution process is exothermic
If the sum of the endothermic terms is greater in magnitude than the exothermic term, then is
positive and the solution process is endothermic.
Aqueous Solutions and Heats of Hydration
Heat of hydration ( = enthalpy change that occurs when 1 mol of the gaseous solute ions is
dissolved in water. Always negative/ exothermic for ionic compounds
1. Exothermic process ( = -)
2. Endothermic process (
3. Neither Exo/Endothermic (
14.4 Solution Equilibrium and Factors Affecting Solubility
Initially the rate of dissolution far exceeds the rate of recrystallization
As concentration of dissolved increases, rate of recrystallization also increases
Dynamic equilibrium = rates of dissolution and recrystallization become equal
Saturated solution = solution in where dissolved solute is in dynamic equilibrium with the solid solute
Unsaturated solution = A solution containing less than the equilibrium amount of solute
Supersaturated solution = solution containing more than the equilibrium amount of solute
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The Effect of Temperature on the Solubility of Solids
The solubility of most solids in water increases with increasing temperature
Recrystallization = enough solid is added to water to create a saturated solution at an elevated
temperature. It is a common way to purify a solid
Crystalline structure tends to reject impurities, resulting in purer solid
Factors Affecting the Solubility of Gases in Water
Solubility of a gas in a liquid is affected by both temperature and pressure
The Effect of Temperature
The solubility of gases in liquids decreases with increasing temperature
The Effect of Pressure
The higher the pressure of a gas above a liquid, the more soluble the gas is in the liquid
Henry’s law: Sgas = kHPgas
14.5 Expressing Solution Concentration
Dilute solution = contains small quantities of solute relative to the amount of solvent
Concentrated solution = contains large quantities of solute relative to the amount of solvent
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Document Summary

Concentrated solutions have a lower freezing point then pure liquids. Solution = a homogeneous mixture of two or more substances or components. Particles of the solvent interact with particles of the solute through intermolecular forces. Aqueous solutions = water is the solvent, and solid, liquid, or gas is solute. Solubility = the amount of the substance that will dissolve in a given amount of solvent. Formation of a solution does not necessarily lower potential energy of constituent particles. We cannot think of the missing of two ideal gases as lowering their potential energy. Entropy = measure of energy randomization or energy dispersal in a system. When the barrier is removed the gases have more dispersal or entropy than when separated. The pervasive tendency for energy to spread out, or disperse, whenever it is not restrained from doing so is the reason two ideal gases mix. Intermolecular forces between (a) solvent and solute, (b) solvent particles themselves (c) solute particles themselves.